1. Field of the Invention
Exemplary embodiments of the present invention relate to a transmit power control method and apparatus in a wireless LAN (WLAN) system; and, more particularly, to a transmit power control method and apparatus which controls a transmit power by using a path loss between a station and an access point (AP) in a WLAN system.
2. Description of Related Art
In a wireless communication device, a transmission terminal requires 2-2.5 times larger power consumption than a reception terminal, and the power consumption required by the transmission terminal depends significantly on the magnitude of transmit power. In general, a commercial wireless LAN device focuses on the transmission performance rather than the power consumption. Therefore, when transmitting a frame, the commercial wireless LAN device sets a transmit power to the maximum transmit power.
When a portable device uses the maximum transmit power, the power consumption efficiency of a wireless station may become a problem. A dynamic transmit power control function of the wireless communication system for the power consumption efficiency may not only reduce battery consumption, but also improve the immunity to interference.
Conventionally, research has been conducted on a transmit power control method between a station and an AP or between a station and a station. However, an algorithm combined with transmit rate control is required in terms of link control, and a transmit power control scheme is required in which a hidden node problem and a basic service set (BSS) network unit are simultaneously considered.
The hidden node problem occurs when a signal transmitted from a specific station within a basic service set suffers from a path loss caused by a channel and does not approach the receive sensitivity of another station. In this case, when a station occupies a channel, another station may not recognize the occupation. Furthermore, as another station attempts to transmit a signal, signal collision may occur. In order to minimize the hidden node problem, ready-to-send (RTS) and clear-to-send (CTS) frames are used. After the RTS and CTS frames are transmitted at the maximum power, a station may occupy a channel and acquire a transmit opportunity. In this case, the station may transmit data at a proper transmit power during the acquired transmit opportunity.
During frequent data communication processes, the exchange of RTS and CTS frames using the maximum transmit power may serve as a main factor which reduces the throughput efficiency and power consumption efficiency of a wireless station. Furthermore, the performance of a station included in the radio range of an AP belonging to different BSSs may be reduced, and the performance of another station may be reduced by a station belonging to an overlapping basic service set (OBBS). In a case of the next-generation WLAN system, the bandwidth may be widened, and a multi-mode and multi-user scheme may be used. Therefore, it is expected that the interference problem will be serious in the next-generation WLAN system.